I have a horse that does this too. What I’ve found helped is keep a shorter rope to maintain a walk and allow a little more rope to trot, and a bit more for canter. Always keep the head in and hind-end out to stay safe. If the canter becomes to wild, bring your pony in and trot them until they calm. This is what I’ve found helps.
Maybe instead of lunging her try free lunging her. I would only do this in an enclosed, indoor riding arena and give her room to freak out or buck. I would also make sure you are prepared for her to go a little bit crazy.
Hope this helps!